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To develop a technique for molt stimulation in shrimp, the Molt Inhibiting Hormone of the banana shrimp Fenneropenaeus merguiensis (FmMIH) has been cloned and characterized.  The mature peptide of FmMIH consists of 76 amino acid residues, a glycine residue at position 10 of the mature peptide, 6 cysteine residues located in the relative identical conserved position of the mature peptide.  In addition to the eyestalk, high level of FmMIH transcript can be detected in the intestine.  During the molting cycle, FmMIH transcript level was low throughout the post-molt, early to mid-intermolt and premolt stages.  However, a sharp increase was observed in late intermolt (C3 stage).  Both alignment and phylogenetic tree analysis revealed that FmMIH is most similar to MIH of other shrimp species.  To perform the functional assay, double stranded RNA for FmMIH was prepared and injected into juvenile shrimp.  A significant reduction of 2.3 days (P<0.05) in molt cycle duration was observed in shrimp receiving dsMIH injection. Interestingly, injection of recombinant FmMIH also caused a significant (P<0.05) reduction in the molt cycle duration. We have hypothesized that the recombinant protein is biological inactive but it can compete with the endogenous MIH for carrier protein binding and consequently reduce the amount of MIH that could reach the targets.  The molt cycle shortening is probably in response to the increase in ecdysteroid titer after MIH inhibition is relieved.  It is then followed by an increase in ecdysone receptor expression for molt advancement.  In conclusion, the result of this study will provide new insight for the manipulation of molting in decapod.

Supported by the National Science Foundation of China (NSFC# 31572606

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